Endotoxin or lipopolysaccharide (LPS), released from the cell wall of bacteria, plays a central role in a broad spectrum of human disease. The pathogenic importance of LPS in gram-negative sepsis is well established. Intravenous LPS induces all of the clinical features of gram-negative sepsis, including fever, shock, leukopenia followed by leukocytosis, and disseminated intravascular coagulation (Favorite et al., J. Clin. Invest. 21:589 (1942)). Higher concentrations of circulating levels of endotoxin have been associated with manifestations of systemic inflammatory response syndrome (Wang et al., Clin. Nucl. Med. 20:494 (1995)) and the development of acute respiratory distress syndrome following sepsis (Brigham et al., Am. Rev. Respir. Dis. 133:913 (1986)).
The ability of the host to respond to endotoxin may play an important role in determining the severity of the physiologic and biologic response to this frequently encountered toxin. In mice, genetic differences in susceptibility to LPS have been established. Several reports suggest that humans may also respond differently to LPS. LPS is thought to cause much of its morbidity and mortality by activating kinases (DeFranco et al, J. Steroid Biochem. Mol. Biol. 65:51 (1998)) that control the function of transcription factors (nuclear factor-κB ans AP-1) and ultimately lead to production of pro-inflammatory cytokines and co-stimulatory molecules (Wright et al, J. Exp. Med. 189:605 (1999)). Several lines of evidence suggest that the toll receptor (TLR) family, specifically TLR4 and TLR2, regulate the interaction between LPS and intracellular kinases and may serve as a proximal target to interrupt LPS signaling (Wright et al, J. Exp. Med. 189:605 (1999), Medzhitov et al, Nature 388:394 (1997)). Both TLR4 and TLR2 activate signaling through NP-κB and AP-1 in transfected human cell lines (Medzhitov et al, Nature 388:394 (1997), Yang et al, Nature 395:284 (1998)), TLR4 mediates LPS induced signal transduction (Chow et al, J. Biol. Chem. 274:10689 (1999)). CD14, a glycosylphosylphosphatidyl inositol-linked receptor that binds LPS, enhances LPS induced TLR2 (Yang et al, Nature 395:284 (1998)) and TLR4 (Chow et al, J. Biol. Chem. 274:10689 (1999)) signaling, suggesting that the toll receptors interact with CD14 to initiate the cellular response to LPS. Studies in mice indicate that i) the TLR4 gene maps to the critical region in LPS hyporesponsive mice (Poltorak et al, Science 282:2085 (1998)), ii) mutations in the TLR4 gene (Poltorak et al, Science 282:2085 (1998); Qureshi et al., J. Exp. Med. 189:615 (1999)) are found in mouse strains (C3H/HeJ and C57BL10/ScCr) that are defective in their response to LPS, and iii) disruption of the TLR4 gene results in a LPS hyporesponsive phenotype (Hoshino et al, J. Immunol. 162:3749 (1999)). The human TLR4 gene has been shown to be polymorphic and a sequence polymorphism in the TLR4 gene has been shown to be associated with a hyporesponsive LPS phenotype in humans that interrupts LPS signaling (WO 00/77204). Recent characterization of common human TLR4 mutations demonstrates a highly variable efficacy of LPS signaling and capacity to elicit inflammation in humans (Arbour et al, Nat. Genet. 25:187 (2000)).